Electromagnetic hammer



Aug. 23, 1960 P. A. MACCHIONI ET AL ELECTROMAGNETIC HAMMER 5 Sheets-Sheet 1 Filed May 19, 1958 g- 1950 P. A. MACCHIONI ETAL ,9 9,909

ELECTROMAGNETIC HAMMER Filed May 19, 1958 5 Sheets-Sheet 2lllllllllllllll l fllllllllllwillllll mmm lllllllll llllllllll 1 Aug,23,1960

Filed May 19, 1958 P. A. MACCHIONI ETAL ELECTROMAGNETIC HAMMER Fig. 7

5 Sheets-Sheet 3 1960 P. A. MACCHIONI ETAL 2,949,909

ELECTROMAGNETIC HAMMER Filed May 19, 1958 5 Sheets-Sheet 4 l 1950 P. A.MACCHIONI ETAL 2,949,909

ELECTROMAGNETIC HAMMER Filed Kay 19, 1958 5 Sheets-Sheet 5 United StatesELECTROMAGNETIC HAMMER Pietro Aurelio Macchioni and Luigi Macchioni,both of Piazza Statute, Turin, Italy This invention relates to anelectromagnetic hammer of the type in which the striker adapted to acton the end or spigot of .a tool supported by the hammer casing, issecuredly fixed to the movable portion of the armature of anelectromagnet, the stationary portion of which together with theenergizing winding are mounted in the hammer casing, resilient means,preferably helical metal springs being provided to oppose the attractionon the movable portion of the electromagnet armature, therebydetermining the width of the gap or gaps where the electromaguetcomprises in a well-known manner a three-branch armature, two branchesembracing from the outside the coil, and a central branch beingsurrounded by the coil. In this known hammer construction both thestriker and tool spigot are guided on their rectilinear reciprocatingmotion in suitable guides or bushes, so that it was essential to providefor periodic adequate lubrication of the sliding parts of the hammer bysuperior lubricants, more particularly lubricants resisting hightemperatures (up to 140 C.) on account of the heavy work and stresses towhich the said sliding parts are subjected.

The necessity of providing for periodic adequate lubrication of thehammer was per se a serious drawback and did not fully avoid the stillmore serious inconvenience deriving from the fact that both the strikerand tool spigot slide in suitable guides provided in the hammer frame.Now, it is known that however perfect the sliding surface in thedirection of the striker axis may be, friction cannot be fully avoided,since a quick reciprocating motion is involved apart from the brakingeffect due to magnetic leakage and ensuing magnetization of the movableparts. A further cause of friction at this region resides in a smalltorque set up periodically at the compression stage of theopposingspring acting on the striker. A further friction set up during operationof the hammer is generated between the tool spigot and its guide fastwith the hammer frame or tapped collar in which the spigot is inserted.Experiments carried out on a number of unsatisfactorily lubricatedhammers disclosed that the said friction leads to a loss in efliciencyup to 50%. This can be explained by considering that, assuming one gramfriction only on each striker stroke which performs 3000 up to 6000strokes/minute, most of the power employed for performing .a certainwork is consumed merely for overcoming the said friction. It was foundthat an insufficient lubrication may lead to a reduction in stroke ofthe striker such that the striker no longer strikes the tool. Thisannuls the hammer efliciency and gives rise to objectionable wear of thesliding surfaces. Further drawbacks reducing efliciency of knownelectromagnetic hammers are attributable to the unsatisfactory structureof the magnetic circuit of the electromagnet or, better said, theelectric motor driving the hammer. In fact, eleotromagnets employed fordriving electromagnetic hammers ,or'similar devices have their gapsextending perpendicular ;to the energizing coil axis,-which reducesatent attraction between the movable and stationary portions of thearmature as flux is set up, or at an oblique direction with respect tothe coil axis and direction of flow, or even of curvilinear shape.Though the latter arrangement is more advantageous at the initialattraction stage, it is no longer so at the end stage, on account of thefact that one component only extending in the direction of the coil axisor flux of the attraction force between the movable and stationaryarmature portions can be exploited.

This invention provides an improved electromagnetic hammer fullyeliminating the above drawbacks which can be operated without anylubrication, the said hammer practically fully avoiding the frictionsources mentioned above, so that the hammer can be operated without anylubrication, and maintain a high effectiveness and increased emciencyowing to the absence of passive resistances, this resulting inconsiderable economy in operating costs.

A further object of this invention is to provide an electromagnetichammer, the magnetic motor of which is equipped with a magnetic circuitof the improved structure adapted to minimize any loss in eificiencyfrom the electric hammer part and aiford an optimum synchronism betweenthe displacements of the movable portion of the electromagnetic armatureand variations in magnetic flow.

A further purpose of this invention is to provide an electromagnetichammer which is simple in construction, of low weight and at the sametime sufliciently tough for withstanding heavy operating conditionsimposed thereon.

A further purpose of this invention is to provide an electromagnetichammer which can be operated with a satisfactory efficiency both onshort and long strokes of the strikers at .frequencies of 3000 up to6000 strokes/ minute, provided that the current frequency is 50 periods,and further employed for uses for which electromagnetic vibrators onlywere suitable.

According to this invention, the above purposes are attained bysuspending the striker, movable portion of the electromagnet securedlyfixed thereto within the hammer frame by means of eight springs, out ofwhich four rear springs or opposing springs are adapted to space themovable portion of the armature from the stationary portion thereof anddetermine the width of the gap, the four or synchronizing springs beingadapted to support the movable portion and follow the striker on its onand return stroke avoiding the latter from being released at any momentof its stroke.

A further object of this invention is to arrange the magnetic circuit ofthe electromagnet in such a manner that the outer gaps at least comprisea rectilinear portion extending perpendicular to the coil axis followedby a curvilinear portion, the gaps provided in the outer armaturebranches being arranged at the region situated between the striker andadjacent end of the energizing coil, the inner gap being spaced from theother coil end by an extent which is about /3 the overall coil length.

The above and further characteristic features and advantages will beclearly understood from the appended description referring to theaccompanying drawings which show by way of a non-limiting example someembodiments of the invention.

On the drawings:

Figure 1 is .a longitudinal section of one embodiment of theimprovedhammer,

Figure 2 is a part sectional elevational view of the hammer shown inFigure 1 looking over the arrow F,

Figure 3 is a view from below of the hammer shown in Figure 1,

Figure 4 is a sectional view on line IV-IV of Figure 1,

Figure 5 is a side view of a constructional detail of thehammer,

' Figure 6 is a plan view of the detail shown in Figure 5, v Figure 7 isa longitudinal sectional view of a further hammer embodiment,

Figures 8 and 9 are side views of two tools adapted to be fitted to thehammer shown in Figure 7,

Figure 10 is a lateral part sectional elevational view of a furtherembodiment of the improved hammer,

Figure 11 is a plan view of the tool connected with the hammer shown inFigure 10.

Figure 12 shows a constructional detail of a modification of the hammershown in Figure '10,

Figures 13 to 15 show diagrams of the operation of the improved hammer,

Figure 16 is a side view of a further constructional detail of amodification of the hammer,

Figures 17 and 18 are part longitudinal sectional views of two furthermodifications of the hammer.

As shown in Figures 1 and 2 of the drawings, the hammer casing comprisesa rear portion made up of two symmetrical members 1, 2, respectively,interconnected by a pair of nuts and bolts 3 and 4.

The portions 1, 2, are each formed with a rear extension shaped topartly form the handle 5 which supports a suitably positioned pressbutton 6 acting through the spring 6a and a plunger 6b on the switch 7secured to a body 8 of insulating material arranged at the bottom of theinside of the casing.

A connection 9 is situated at the level of the insulating body 8 on theremote side of the switch 7, for attachment of a current supply cable10.

An energizing coil 11 is arranged within the casing portion formed bythe members 1 and 2 coaxially with the longitudinal hammer axis. Thecoil 11 rests on the remote side of the handle 5 against the walls 12transversely extending beyond the members 1, 2 and carrying on topperforated flanges which are connected by pairs by means of joints 13 tonuts and bolts visible in Figures 2 and 4.

The coil 11 rests on the remote side of the walls 12 on the stationaryportion of the armature of the electromagnet, comprising a bundle ofsheets and having an inner branch or countercore 14 and two outerbranches 13 extending between the outer coil periphery and inner wallsof the members 1 and 2. The movable armature, likewise comprising abundle of sheets insulated from one another, has an inner branch 15 ormovable core of the electromagnet and its outer branches 16 made of onepiece with the core 15. The bundle of sheets forming the movablearmature 16, 15 is arranged on the remote side of the counter-core 14 ina recess in the rear portion of the striker 17. The gaps between thecounter-core 14 and movable core 15 and outer branches 13, 16,respectively of the stationary and movable armature are arranged andshaped to afford a maximum efficiency in operation of the hammer at anytime. As shown in Figure 1 each gap comprises a straight portionextending transversely of the coil axis and a curvilinear portion. Theexperiments carried out disclosed that the best efficiency is obtainedwhen the ratio of length taken across the coil axis of the rectilinearto the curvilinear gap portion is about 1:4. The air gaps are arrangedin a novel manner with respect to the coil 11. The air gap 34 betweenthe core 15 and counter-core 14 is spaced from the coil and bearing onthe stationary armature by about one third of the axial coil length. Theresult is that the movable core 15 of the movable portion is encircledby a high number of turns of the coil 11. The outer gaps 35 are fullyoutside the coil, i.e. beneath its end resting on the walls 12 andoutside its outer peripheral outline. This arrangement and configurationof the gaps afford the following advantages:

(1) Any interference between the dispersed flux portions, whichunavoidably arises at the gaps, is avoided;

(2) A considerable eifective component is aiforded at any stage of thehammer operation.

For most of the flux is transferred at the initial stage of the magneticattraction to the curvilinear gap portion, constantly yielding aneffective attraction component tending to overcome the action of theopposing springs 23. At the end stage of attraction most of the flux istransferred to the rectilinear gap portions and, its attractive forcebeing directed in a truly axial direction with high efficiency, therebyaffording full synchronism between the variations in flux and movementsof the movable armature and striker, and minimizing the unavoidabledelay constantly arising between the sinusoidal variation in fiow andmovement of the movable armature and striker.

All the above advantages favourably affect operation of the hammers bothwith long striker strokes (8 to 12 mm. at a speed of 3000strokes/minute) and short strokes (from 5 to 6 mm. at a speed of 6000strokes/minute).

A convenient modification of the outer gaps 34 is shown in Figure 16.This embodiment afforded the best results in practice. The strikerstructure is more clearly visible in Figures 5 and 6, showing the crossrecess 18 receiving the bundle of sheets 15, 16 and four ribs inX-shaped arrangement, each ending by a cylindrical enlargement 2.0. Thecylindrical enlargements are each formed with a through bore and twoslightly conical seats on opposite sides 21, 22, respectively. The endsof four opposing springs 23 bear and are centred in the four seats 21,the seats 22 receiving the ends of four synchronizing springs 24. Thepurpose of these springs will be explained in detail hereafter. The foursprings 23 bear by their other ends on four screwthreaded washers 25fitted in seats 26 formed in the members 1, 2 and screwed on one end ofthe tie-rods 27 extending with a clearance through the bores in theenlargements 20 on the striker reaching beyond the said bores. The endsof the tie-rods 27 extending from the seats 26 have screwed thereon locknuts 28. The ends of the four synchronizing springs 24 remote from theends bearing and centred in the seats 22 are received by similar seatsformed in the washers 29 screwed on a screw-threaded portion of thetie-rods 27. Lock nuts 30 are provided for locking the washers 29. Theend of the rods 27 remote from the bolts 28 has screwed thereon afurther bolt 31 securing the lower portion of the hammer body or cap 32which closes from the outside the striker 17 and synchronizing springs.

The X-shape of the striker improves cooling of the coil by setting up anefiicient air draught flowing to the inside of the coil and issuingthrough a plurality of holes in the casing on the near side of thehandle 5. The cap 32 has a seat 33 formed in its central forwardportion, said seat receiving the bush or tapped collar 134 for the toolsecured to the cap 32 by means of bolts 135. The rear portion or spigot360: on the tool 36 is seated within the tapped collar 134. The spigot36a is guided in the collar 134 through the interposition of a speciallinear ball bearing comprising a plurality of ball rows 37 mounted in atubular cage 38. Grooves 39 are cut in the outer periphery of the spigot36a and guide the balls 37 therein. Similar guides can be provided inthe inner periphery of the tapped collar 134. The linear ball bearingshown in Figure 1 is adopted where the hammers are used for demolitionpurposes, when they operate under particularly heavy conditions and highfrictions arise between the tool spigot and tapped collar as theoperator presses the apparatus by his full weight to drive the tool intothe material or release it therefrom. The adoption of linear ballbearings aifords a reduction of any sliding frictions as may arisebetween the spigot and threaded collar. This was confirmed by actualpractice. The linear ball a bearing can be made otherwise than shown inFigure 1 and may comprise balls arranged in the supporting cage along ahelical path. The latter embodiment is more particularly suitable whenthe tool should be capable of rotating during operation of the hammerabout its own axis. 40 denotes annular flanges on the spigot 36a adaptedto cooperate with the cross pin 41 for preventing accidental slipping ofthe tool oft its location in the collar 134 and preventing access offoreign bodies to the linear ball bearing.

The end of the spigot 36a extends beyond an axial opening in the cap 32into the hammer to contact with the striker 17 as the opposing springs23 return the striker towards the tool on ceasing of the flux. Figure 1shows the striking stage of the tool. The clearance between the flange40 and inner rib 134a on the collar 134 is visible. The opposing or rearsprings 23 are adapted to push the striker forwardly and determine thegap width in the armature of the electromagnet.

The resilient properties of the springs 23 are selected so that thecompression load required for fully compressing said springs issubjected at the end of the striker stroke due to the action of themagnetic attraction during energizing of the coil somewhat greater thanthe force of said magnetic attraction. The resilient properties of thefour forward synchronizing springs 24- are such that these springs acton the striker by a total load lower than the load of the springs 23. Afurther purpose of the set of the above described eight springs is tofollow the striker on its on and re turn stroke, preventing it frombecoming released at any moment during the hammer operation. The abovedescribed structure fully avoids frictions and passive resistances onmovement of the striker during operation of the hammer.

The hammer modification shown in Figure 7 differs from the embodimentdescribed with reference to Figures 1 to 6 in that the central gap 34 isfully rectilinear. This arrangement is of course better suited withshort stroke hammers (stroke length about 8 to mm. and 6000 strikerstrokes per minute).

The above hammer embodiment diflfers from the last described one in thestructure of the tapped collar for the tool. The collar comprises twobushes 42, 43 receiving springs 44, 45 interposed between the oppositecollar ends and collars 40a provided on the tool spigot 36.

The spring 44 is larger in cross section than spring 45 so as to be lessresilient and avoids an untrained operator excessively pressing the toolthereby tending to reduce the striker stroke and unfavourably affectingthe etficiency of the apparatus. The smaller spring 45 is more resilientbut is more strongly compressed in order to hold the tool spigotconstantly backward in the striker direction and ready to be impingedupon by the latter. On impingement the spring 45 which is more resilienteasily yields allowing forward movement of the tool towards the workpiece.

It will be seen from Figure 7 that the tool 36 is actually a tool holderinto which a chisel 46 is inserted by means of a wedge connection.

The chisel could be replaced by other tools, such as for instance a fork48 for vibrating reinforcing iron on casting concrete into moulds, asshown in Figure 8, or a ram 47 for vibrating moulds shown in Figure 9.In the modified hammer embodiment shown in Figure 10, the cap 32 isdeprived of a tool-holding collar and is merely formed with an axialbore for penetration of the spigot of the tool 50 which is directlyconnected with the striker 17.

In the illustrated embodiments the spigot portion extending from the cup32 has connected therewith a tubular member 51 having a tip 51a andprovided with a plurality of lateral wing pairs 52, 53, 54 inclined tothe axis of the tubular member 51.

The last described hammer embodiment together with a peculiar toolserves for vibrating concrete where considerable mass has to be shaken.The provision of the wings 52, 53, 54 allows transmission of vibrationsdirectly to the mass without any loss in power. The vibrations set thesand granules in motion at a frequency which is approximately thefrequency resonant with the hammer. The sharp end 51a of the tube 51facilitates penetration thereof into the concrete mass. In themodification shown in Figure 12 the hammer is of a construction similaras shown in Figure 10. In this case also the tooi is directly connectedwith the striker. However, it comprises a fiat vibrating plate mountedfor oscillation about a pivot 152 journalled in a fork shaped projection153 on the cap 49.

The arm 154- securedly fixed to the plate which forms a bell-crank leverwith the former, is articulated to the end of the spigot 155 secured tothe striker.

Figures 13 and 14 show the variations in flux and feed current for shortstroke hammers (about 5 to 8 mm.) and long stroke hammers (8 to 12 mm.)at frequencies of 6000, 3000 blows, respectively, per minute.

In the diagram shown in Figure 13, the hatched portions of the halfwaves correspond with the attraction periods of the striker, theportions 60 between the attraction periods corresponding with the ropeling periods of the movable armature connected with the striker, at theend of which the striker abuts the end of the tool spigot.

Figure 15 shows a characteristic diagram for the improved hammer of thebehaviour in time of the striker displacements in connection withconcrete vibration. This diagram shows the effectiveness of the blowsupon the tool spigot at the end of the striker repelling stroke.

In the modified embodiments shown in Figures 17 and 18 the striker 1'7is held between two springs 81, 82, respectively. The spring 81 is ahelical spring and is interposed between an annular projection of thestriker 17 and the bottom of the forward casing 32. secured by means ofnuts 83 and bolts 84 to the hammer body. The spring 32 is a conicalspring and is interposed between the other side of projection 80 of thestriker 17 and an annular seat 85 hearing on the stationaryelectromagnet portion 13. This structure which employs a conical spring82 having its larger diameter end facing the electromagnet, aifords thefollowing important advantages:

(1) The conicity of the spring affords a small size structure at thehammer end supporting the tool as well as shortening of the overallhammer length, for a portion of the movable core 15, 16 can be arrangedwithin the outline of the spring 82. In this case the structure of thelateral gaps can be conveniently selected of the type shown in Figure16.

(2) Should the spring 32 break, the hammer is automatically arrested,for the conicity of the spring causes the portions 14 and 15 of theelectromagnet armature to readily abut each other.

The embodiment shown in Figure 18 is advantageous where a hammer with alonger stroke of the striker 17 is desired without increasing the gaps.This purpose is attained by making the central electromagnet core 15similarly to Figure 17 as well as the counter-core 14 of a movable typeand causing the latter to bear on a reaction spring 86. In order toreduce the lateral gaps the core 15 and counter-core are guided byrectilinear bearings 88 quite similar to the bearing shown in Figure 1adapted to guide the tool tail, Since during operation of the hammer thecore 15 and counter-core 14 abut each other, they are provided at theirfacing ends with rims in the form of rings 87, 89 of highly resilientand tough antimagnetic material in order to reduce the core wear.

What we claim is:

1. An electromagnetic vibrator comprising a portable casing having ahandle secured at one end and an opening provided in its other end, acoil coaxial with said openmg inside said casing arranged near the endof the latter opposite said opening, a magnetic core for said coilextending through-the latter, a complementary stationary armatureembracing said coil from the outside, at least a part of said corefacing said opening in the casing being movable in the axial directionof said coil, a striker inside the casing arranged between said coil andsaid opening, said striker being fast with said movable part of thecore, a first and a second set of four springs symmetrically arrangedaround the common axis of said coil and said opening, the springs ofboth sets bearing each by its one end on a seat provided in the strikerbody, the other end of each spring of said first set hearing by itsother end on a seat provided inside said casing near said coil and theother end of each spring of said second set bearing by its other end ona seat provided inside said casing near said opening, and means arrangedat the end of said casing in which said opening is provided forsupporting and guiding the end of a tool to be acted upon by thestriker.

2. An electromagnetic vibrator comprising a portable casing having ahandle secured at one end and an opening provi ed in its other end, acoil coaxial wtih said opening inside said casing arranged near the endof the latter opposite said opening, a magnetic core for said coilextending through the latter, a complementary stationary armatureembracing said coil from the outside, at least a part of said corefacing said opening in the casing being movable in the axial directionof said coil, a striker inside the casing arranged between said coil andsaid opening, said striker being fast with said movable part of thecore, a first and a second. helical spring wound around said striker, acollar on the central portion of said striker, a pair of annular seatsat opposite sides of said collar each for abutting one end of saidsprings, a seat for abutting the other end of said first spring situatedinside said casing near said coil and a seat for abutting the other endof said second spring situated inside said casing near said opening,said first spring being arranged between said collar and said seat nearsaid coil being of conical shape and having its end of larger diameterabutting on said seat lying near said coil, a linear bearing comprisinga bush fast with the casing and surrounding a portion of the striker andseveral ball rows extending parallel with the bush axis and held by acommon cage, said balls of each row being guided in grooves providedinside said bush and on the outer periphery of said portion of thestriker, and means arranged at the end of said casing in which saidopening is provided for supporting and guiding the end of a tool to beacted upon by the striker.

3. An electromagnetic vibrator as set forth in claim 2, having in frontof said movable part of the core fast with the striker a counter-coremovable in the axial direction of the core, a linear roll bearing forsupporting and guiding the end of said counter-core opposite said partof the core fast with the striker and a spring interposed between saidend of the counter core supported by said linear bearing being furtherprovided for guiding the counter-core and for permitting the latter toyield under impacts it may receive from the movable core part fast withthe striker during operation of die vibrator.

4. An electromagnetic vibrator comprising a portable casing having ahandle secured at one end and an opening provided in its other end, acoil coaxial with said opening inside said casing arranged near the endof the latter opposite said opening, a magnetic core for said coilextending through the latter, a complementary stationary armatureembracing said coil from the outside, at least a part of said corefacing said opening in the casing being mavoble in the axial directionof said coil, a striker inside the casing arranged between said 8 coiland said opening, said striker being fast with said movable part of thecore, a first and a second set of four springs symmetrically arrangedaround the cornmon axis of said coil and said opening, the springs ofboth sets bearing each by its one end on a seat provided in the strikerbody, the other end of each spring of said first set bearing by itsother end on a seat provided inside said casing near said coil and theother end of each spring of said second set bearing by its other end ona seat provided inside said casing near said opening; a tool holdercollar secured to the part of the casing in which said opening isprovided, said collar being coaxial with said opening, a linear bearingcomprising a ball row within said collar, a tool having its one endintroduced in said casing through said collar and said opening, saidbearing supporting and guiding the said end of a tool which isintroduced through said opening in said casing for receiving impactsfrom the striker, and a cage for holding said balls aligned in rowsparallel to the axis of said collar, the inner wall of said collar andthe outer Wall of said tool end having provided therein axial groovesforming rolling tnacks for said balls.

5. An electromagnetic vibrator comprising a portable casing having ahandle secured at one end and an opening provided in its other end, acoil coaxial with said opening inside said casing arranged near the endof the latter opposite said opening, a magnetic core for said coilextending through the latter, a complementary stationary armatureembracing said coil from the outside, at least a part of said corefacing said opening in the casing being movable in the axial directionof said coil, a striker inside the casing arranged between said coil andsaid opening, said striker being fast with said movable part of thecore, a first and a second set of four springs symmetrically arrangedaround the common axis of said coil and said opening, the springs ofboth sets bearing each by its one end on a seat provided in the strikerbody, the other end of each spring of said first set bearing by itsother end on a seat provided inside said casing near said coil and theother end of each spring of said second set healing by its other end ona seat pro vided inside said casing near said opening, a tool holdercollar secured to the part of the casing in which said opening isprovided and coaxial to the latter, annular bent in flanges at the endsof the collar, two springs inside said collar each bearing on one ofsaid flanges, a tool having its one end introduced inside said casingthrough said collar and said opening for receiving impacts from saidstriker, tWo spaced flanges at the portion of said tool end arrangedinside said collar for abutting the other ends of said springs bearingon said annular flanges, said spaced flanges having an outer diametersmaller than the inner diameter of said collar.

6. An electromagnetic vibrator comprising a portable casing having ahandle secured at one end and an opening provided in its other end, acoil coaxial with said opening inside said casing arranged near the endof the latter opposite said opening, a magnetic core for said coilextending through the latter, a complementary stationary armatureembracing said coil from the outside, at least a part of said corefacing said opening in the casing being movable in the axial directionof said coil, a striker inside the casing arranged between said coil andsaid opening, said striker being fast with said movable part of thecore, a first and a second set of four springs symmetrically arrangedaround the common axis of said coil and said opening, the springs ofboth sets bearing each by its one end on a seat provided in the strikerbody, the other end of each spring of said first set bearing by itsother end on a seat provided inside said casing near said coil and theother end of each spring of said second set hearing by its other end ona seat provided inside said casing near said opening, a tool having theform of a tubular rod having its one end 9 introduced in said casingthrough said opening, means for securing said end of the tool to saidstriker, a plurality of lateral wing pairs inclined to the axis of saidtubular rod secured to the part of the latter projecting outwardly ofsaid casing.

7. An electromagnetic vibrator comprising a portable casing having ahandle secured at one end and an opening providing in its other end, acoil coaxial with said opening inside said casing arranged near the endof the latter opposite said opening, a magnetic core for said coilextending through the latter, a complementary stationary armatureembracing said coil from the outside, at least a part of said corefacing said opening in the casing being movable in the axial directionof said coil, a striker inside the casing arranged between said coil andsaid opening, said striker being fast with said movable part of thecore, a first and a second set of four springs symmetrically arrangedaround the common axis of said coil and said opening, the springs ofboth sets bearing each by its one end on a seat provided in the strikerbody, the other end of each spring of said first set hearing by itsother end on a seat provided inside said casing near said coil and theother end of each spring of said second set bearing by its other end ona seat provided inside said casing near said opening, a rod secured tothe striker and projecting outwardly from said casing through saidopening, a bell crank lever having an arm hinged to the end of said rodprojecting from said casing, a pin for rockingly supporting saidbell-crank lever fast with the casing end at which said end is provided,said pin having its axis perpendicular to the axis of said opening andbeing laterally offset with respect to the latter, a blade secured tothe other arm of said bell-crank lever, said other arm extendingnormally parallel with the axis of said opening.

References Cited in the file of this patent UNITED STATES PATENTS2,380,622 Weyandt July 31, 1945 2,399,977 Bardos May 7, 1946 2,436,992Ernst Mar. 2, 1948 2,439,230 Weyandt et a1. Apr. 6, 1948 2,641,720Stewart June 9, 1953 FOREIGN PATENTS 614,242 Great Britain Dec. 13, 1948741,536 Great Britain Dec. 7, 1955

